Cavity resonator electrondischarge device



June 19, 1951 w. c. BROWN f 2,557,780

cAvITY RESONATOR RLEc'rRoN DISCHARGE DEVICE Filed April 19, 1947 2 Sheets-Sheet ly June 19, 1951 w. c. BROWNY oAvITY RESONATOR ELEc'rRoN DISCHARGE DEVICE Filed April 19. 1947 2 Sheets-Sheet 2 rn/2MB FIG. /0

Patented June 19, 1951 UNITED CVITY RESONATOR ELECTRON- DSCHARGE DEVICE William C. Brown, Lincoln, Mass., assigner to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application April 19, 1947, Serial No. 742,541

7 Claims.

' This invention relates to electron discharge devices having a, plurality of cavity resonators, and more particularly to those for generating oscillations of short wave length.

One of the objects of the present invention is to provide a device of the type referred to which shall have an improved symmetrical coupling for all of the cavity resonators, by which the ratio of energy actually delivered, to that generated by the device, is materially increased.

The above object and such other aims and objects of the present invention as may hereinafter appear will be best understood from the following description, taken in connection with the accompanying drawings of several embodiments of the invention herein presented for illustrative purposes.

In the drawings? Fig. l is a central, longitudinal section of an electron discharge device, as viewed along line I"-I of Fig. 3, incorporating one illustrative embodiment of the invention; A Fig. 2 is a partial, longitudinal section of an electron discharge device incorporating a, second illustrative embodiment of the present invention;

Fig. 3 is a horizontal cross-section on line 3,-3 of Fig. 1;

Fig. 4 is a perspective view showing the energy transferring means of the output coupling and how it cooperates with the resonant cavities;

Fig. 5 is a, partial longitudinal section of an electron discharge device incorporating a third illustrative embodiment of the present invention;

Figs. 6 and '7 are schematic diagrams of equivalent circuits of the electron discharge device;

Fig. 8 is a sketch of the embodiment shown in Fig. 5 for the purpose of mathematical calculations utilized to determine the electrical connections of the electron discharge device;

Fig. 9 is an equivalent circuit of the sketch shown in Fig. 8; and

Fig. 10 is a view along the aXis of the electron discharge device illustrated in Fig. 8 showing the relative disposition of the prongs of the energytransferring means for purposes of mathematical calculations.

The invention is herein illustratively shown and described in its application to that type of electron discharge device known as a magnetron.

Referring now to Fig. 1, there is shown a cylindrical member I0 having soldered to its inner surface a plurality of suitably spaced, radially disposed anode arms EI, the inner edge surfaces of which constitute anode faces I2. Said cylindrical member and anode arms are preferably made of copper and said anode surfaces are disposed substantially parallel to an electron-emissive cathode I3. For example, said cathode may be a slotted tungsten cylinder suitably supported 2 axially of said anode surfaces. Each pair of said anode arms li, with the intervening portion of said cylindrical member I, constitutes a cavity resonator i4, see Fig. 3.

The cylindrical member Iii is hermetically sealed at both ends, thus forming a hermetically sealed envelope or enclosure. In the illustrative embodiment of Fig. 1, a disc member I 5 and vitreous member I6 are used to complete the aforementioned envelope. The member I5, preferably constructed of copper, is suitably apertured, as at I8, to receive, as by soldering, a tubular member I'I, or the disc I5 and tubular member il may be constructed as a unitary member.

Concentrically disposed within said cylindrical member are a pair of pole pieces ISI-20. Said pole pieces are partially cylindrical and partially the frustum of a cone. The smaller of the two parallel areas of said frustun'i serves to concentrate any magnetic field present between said pole pieces, The pole piece I9 is disposed within that portion of the envelope providing ingress for a cathode lead-in and supporting member ZI. Both of the pole pieces are provided, respectively, with bores Z2- 23, the bore 22 being in register with the aperture I8. The other pole piece 2D is disposed Within an electrically conductive member in the form of a cylindrical cap 2Q. lSaid cap is preferably made of copper, the open end being disposed in slotsl I IA provided in alternate anode arms Ii. Integral with the flat portion 25 of said cap is the open end of an electrically conductive tubular member 25, preferably made of copper. The opposite open end of said tubular member is hermetically sealed along its edge in an `aperture 2'! in the vitreous member I6, the particular arrangement just described being adapted to receive an inner conductor 2'8 of a coaxial transmission line comprising said inner conductor 28 andan outer conductor 29. Intermediate said outer conductor 2S and the envelope IG is a, tubular member 3U. This tubular member is adjusted so that, between points A and B, the distance is equal to a half wavelength of the operating frequency of the electron discharge device. When so adjusted it serves in the capacity of a radio frequency choke in a manner well known to those skilled in the art to which it pertains.

If the above-described device be energized and a longitudinal field be excited within the device by suitable means, as for example by supplying lsaid pole pieces I 9-26 with a magnetic Ifield from an external magnet, oscillations will be generated in the cavity resonators Il `which may be led out of the device to a suitable utilizing circuit by means of the novel coupling device just described, comprising the cap '2.4 :and tubular member 26.

In operation, the polarity of the anode arms Il is constantly shifting, alternate arms being always of the opposite polarity to that of the intervening arms. By its connection :with the alternate arms, the coupling cap 24 transfers the energy of said alternate arms to the tubular member 25 and thence to the inner conductor 28, while that from the intervening anode arms is transferred through the envelope l, the tubular member 3B to the outer conductor 29. `Since said conductors 28 and 29 form the inner and outer conductors, respectively, of a coaxial line, the energy collected by said coupling cap 24 is caused to flow out due to the difference of potential of said two conductors.

Fig. 2 is an alternative embodiment adapted for connection to a wave guide system. In this particular embodiment, the cap 24 is surmounted by a dome-shaped cap 3l which may serve as an exciting probe for a wave guide in a manner familiar to those versed in the art. A vitreous member also formed in the shape of a dome 32 serves to hermetically seal the upper portion of the cylindrical member I0. The above-described embodiment of the present invention is adapted to be directly inserted in a wave guide section of a wave guido system and when properly energized, as hereinbefore described, 'will propagate such energy through said wave guide system.

Fig. 3 is a cross-sectional View taken along line 3-3 of Fig. 1 and clearly details the relative position of the cap 24 with respect to the anode arms Il. It also illustrates the manner in which said cap 24 is attached to the alternate anode arms Il by means of the slots HA. A pair of electrically conductive straps 32-33 are connected,

respectively, to the alternate and intervening anode arms to arrest the generation of spurious oscillations.

Fig. 4 is a prspective View of the invention wherein, for the sake of clarity, only a portion of the anode arms II are shown, together with a fragmentary view of the cap 24 and the tubular member 2S surmounting same. Here is clearly indicated the manner in which the cap 24 is disposed in the slots HA provided in the alternate anode arms Il. A second pair of electrically conductive straps 34-35, substantially identi cal with straps 32 and 33, are connected, respectively to alternate and intervening anode arms.

Fig. 5 represents a third embodiment of the present invention. Whereas, the rst and second embodiments were adapted to magnetrons, for example which employ twenty anode arms or less, it is necessary in the case of magnetrons employing more than twenty anode arms that the coupling cap 24, Figs. l and 2, be smaller in its diametrical dimensions as the number of anode arms employed are increased beyond, for example, twenty arms. How the proper dimensions are arrived at will be discussed in connection with Figs. 6, 7, 8, 9, and 10.

In this third embodiment, the reduction of the diametrical proportions of the coupling cap makes its necessary to alter the type of pole piece used. It was found necessary to provide a pole piece 40 and a coupling cap 4I of the type illustrated. It Will be appreciated that as the coupling cap dimensions were made smaller its was no longer possible to dispose the pole piece within said coupling cap because the gap between said pole piece and the external magnetizing means, not shown, would increase the reluctance path considerably. As a result of such increase in reluctance, the external magnetizing means would begin to as- 4 sume proportions which would be bulky and une economical.

To overcome the aforesaid obstacles, the pole piece 40 was provided with a plurality of apertures 42 and the coupling cap 4| with an equal number of prongs 43 of suitable dimensions to enable them to pass freely, and without touching, through the apertures 42, the ends of said prongs being connected to the anode arms Il within slots 44 provided therein. The pole piece 40 was made in the form of a thick shallow dish with an aperture 45 in the bottom thereof, said aperture being in register with the opening formed by the inner edges 46 of the anode arms I I. The aperture 45 permits one end of the cathode structure, see Fig. 1 to extend therethrough. The upper edge 41 of said pole piece is soldered within the cylindrical member I0, said member having a substantially thinner wall section 48 at this point of connection.

By providing a thin wall section at this point, the reluctance path, between the pole piece edge 41 and an external pole piece ring 49, is kept to a minimum, when suitable magnetizing means are attached to said pole piece ring 49.

For best results, the dimensions of the coupling cap should be such that the energy stored per cycle in the magnetron will have a certain ratio to the power dissipated in a matched load. This ratio will be designated hereinafter as the QE of an axial output electron discharge device of the type hereinbefore described.

Figs. 6 and 7 illustrate schematically the equivalent circuit of the above-described electron-discharge device in which CT and Lr represent, respectively, the total capacity and inducance associated with said device, while ERF represents the total radio frequency voltage across the aforementioned CTLT combination. RT is the total resistance or external load which will give the desired QE when connected in parallel with said Lr. QE is determined by the following equation RT R1 This may be written =L i RT R,

R r LTRi LT Lf Therefore LTR, QE: mL?

Knowing QE it now remains to determine R1 and L1 as will be presently described.

Fig;v 8 is a sketch of an axial output device of the type herein described, the left-hand view, with respect to the drawing, being a transverse cross-section looking along the axis Q cf the right-hand View from right to left, said righthand view being a longitudinal cross-section taken along line X-X of the left-hand view, while-Fig. 9 represents an equivalent circuit of the sketch in Fig. 8. vWith reference to Fig. 8, rb, 71, Z and Z1, said dimensions are in inches. l, The impedance RL, Fig. 9, at the terminals C-D will be the characteristic impedance of the .coaxial line at points C-D in Fig. A8. The connection for C-D to A-B is made by a plurality of prongs 43 which pass through apertures in the pole piece shown in Fig. 5. The pole piece is not taken into account in any of the calculations above or any to be described presently. RL transformed through the section of line between C-D and A-B becomes the R1 needed to determine QE.

The method used to determine the characteristic impedance, designated herein as Zo, of the section C-D to A-B is as follows.

,Assuming three prongs 43 were used to connect C-D to A-B, the transmission line will appear as illustrated in Fig. 1G when viewed along its axis. Therefore zo: ec 10g Dm ohms where a, b, and c are, respectively, the distances between the centers of the prongs 43, n being equal to the number of prongs and rp the size of the prongs, said size being as small as possible, commensurate with the amount of power the prongs are to carry, in order to minimize the size of the apertures in the pole piece.

In the case of the rst embodiment, wherein the coupling cap 24 was entirely cylindrical, the calculations for determining Ds would be based on the number of anode arms contacted by said cap, each contact being considered a prong. Therefore, for n number of prongs equally spaced on the circumference of a circle of ra- Using RL as a terminating impedance for a coaxial line of characteristic impedance Zo and length Z1, the value of R1 is found by ordinary long line transmission theory. L1 is calculated as follows:

where 30,480 is a numerical constant that 'provides a practical unit (aan), N is the number of anode arms, t is the thickness of said anode arms and the other symbols rb, n and l are dimensional values as indicated in Fig. 8. A value of r1 can now be chosen and L1 and R1 determined, which will yield QE; r1 may now be adjusted to produce the desired QE, remembering that as r1 increases, QE increases.

As a result of the simple and compact structure herein described, the invention provides novel means for transferring energy from each resonant cavity, or any desired number of resonant cavities, without the complicated structure and planning such an arrangement would entail if one were to utilize such means as hairpin type probes and the like.

The embodiments of the present invention which have been illustrated and described have been selected for the purpose of setting forth the principles involved. It will be obvious, however, that the invention may be modified to meet various conditions which may be met with in different specic uses and it is, therefore, intended to cover by the appended claims all such modifications which fall within the spirit and scope of this invention.

' What is claimed is:

l. An electron discharge device comprising: a cathode; an anode structure spaced from said cathode and provided with a plurality of cavity resonators; a first conductor connected to. said anode structure and constituting one of the conductors of a transmission line; a conductive cap connected to one of said cavity resonators in a region of relatively low radio-frequency voltage; and a second conductor electrically connected tol said cap said second conductor constituting the other conductor of said transmission line.

2. An electron discharge device comprising: a cathode; an anode structure spaced from said cathode and provided with less than a critical number of cavity resonators; a first conductor connected to said anode structure and constituting one of the conductorsof a transmission line; a conductive cap connected to one of said cavity resonators in a region of relatively low radio-frequency voltage; and a second conductor electrically connected to said cap said second conductor constituting the other conductor of said transmission line.

3. An electron discharge device comprising: an electrically conductive envelope; said envelope constituting the outer conductor of a transmission line; a cathode mounted within said envelope; a plurality of anode arms extending inwardly from said envelope and surrounding said cathode; each pair of adjoining anode arms, together with that portion of said envelope therebetween, constituting a cavity resonator; an electrically conductive cap, the open end of which is connected to that portion of the alternate anode arms adjacent said envelope; and an electrically conductive tubular member connected exteriorly to the closed end of said cap and constituting the inner conductor of said transmission line.

4. An electron discharge device comprising: an electrically conductive envelope; said envelope constituting the outer conductor of a transmission line; a cathode mounted within said envelope; a plurality of anode arms extending inwardly from said envelope and surrounding said cathode; each pair of adjoining anode arms, together with that portion o1 said envelope therebetween, constituting a cavity resonator; an electrically conductive cap, the open end of which is connected to that portion of the alternate anode arms adjacent said envelope; an electrically conductive tubular member connected exteriorly to the closed end of said cap and constituting the inner conductor of said transmission line; and a pair of pole pieces, the field of which extends longitudinally of said envelope, one of said pole pieces being disposed Within said electrically conductive cap and the other oppositely disposed, with respect to said rstmamed pole piece, Within said envelope.

5. An electron discharge device adapted to be connected to a load having a predetermined resistive impedance comprising: an electrically conductive envelope; a conductor connected to said envelope and constituting the outer conductor of a transmission line; a cathode mounted Within said envelope; a plurality of anode arms extending inwardly from said envelope and surrounding said cathode; each pair of adjoining anode arms, together with that portion of said envelope therebetween, constituting a, cavity resonator; and an electrically conductive member, the open end of which is connected to a point on one of said anode arms, the distance between said point of connection and the axis of said envelope having a predetermined valuev satisfying the equation LTR,

where where in the equation for L1 N=the number of anode arms,

N=the radius of the envelope with respect to its axis,

1-z=the distance between the electrically conductive member and the axis of said envelope,

l=the length of the anode arms parallel with the axis of said envelope, and

t=the thickness of the anode arms, said electrically conductive member constituting the other conductor of said transmission line.

6. An electron discharge device comprising: a cathode; an anode structure, spaced from said cathode, and incorporating a cavity resonator; a transmission line including a pair of conductors electrically connected to spaced points on said cavity resonator; and a pair of pole pieces disposed adjacent said anode structure at opposite ends of said cavity resonator; one of said pole pieces being supported by one of the conductors of said transmission line.

7. An electron discharge device comprising: a cathode; an anode structure, spaced from said cathode, and incorporating a cavity resonator; a transmission line including inner and outer conductors; said outer conductor being electrically connected to the exterior surface of said anode structure, and said inner conductor being provided with a coupling member electrically connected to a point on said cavity resonator; and a pair of pole pieces disposed adjacent said anode structure at opposite ends of said cavity resonator; one of said pole pieces being supported within the coupling member of the inner conductor of said transmission line.

WILLIAM C. BROWN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,414,085 Hartman Jan. 14, 1947 2,429,291 Okress Oct. 2l, 1947 2,435,984 Spencer Feb. 17, 1948 2,442,118 Donal, Jr., et al. May 25, 1948 2,454,337 Okress Nov. 23, 1948 2,478,534 Kather Aug. 9, 1949 

